majnemer added inline comments.
================
Comment at: include/clang/Basic/AttrDocs.td:1736-1755
@@ -1722,2 +1735,22 @@
+
+ // Explicit template definition (in exactly ONE .cpp file)
+ template struct __attribute__((unique_instantiation)) my_template<int>;
+
+
+When the unique_instantiation attribute is specified on an explicit template
+instantiation, the compiler is given license to emit strong symbols for
+this specific explicit template instantiation.
+
+If the attribute is present on one such definition or declaration for a given
+entity, it must be present on all.
+
+Note that to ensure correct execution the user MUST make certain that no
+other translation unit has an implicit instantiation of the same entity. In
+particular this means that any usage of the entity has to be preceeded by an
+appropriate explicit template declaration or definition.
+It is thus recommended that explicit template declarations are placed in
headers
+to suppress any potential implicit instantiation of the entity. In order to
+encourage this programming style, any explicit template definition with this
+attribute MUST be preceeded by an appropriate declaration.
}];
----------------
Instead of using all-caps for emphasis in "ONE" and "MUST", why not bold the
text instead? It would catch the eye a little faster.
================
Comment at: include/clang/Basic/DiagnosticSemaKinds.td:2533-2534
@@ -2531,1 +2532,4 @@
":must be between 1 and %2}2">;
+def err_unique_instantiation_wrong_decl : Error<
+ "'unique_instantiation' attribute only applies to an explicit template
declaration or instantiation">;
+def err_unique_instantiation_no_declaration : Error<
----------------
I can't seem to see any users of `err_unique_instantiation_wrong_decl`.
================
Comment at: lib/AST/ASTContext.cpp:8283-8286
@@ +8282,6 @@
+ Context.containedInUniqueInstantiation(FD)) {
+ // We return GVA_StrongExternal here, instead of going through the logic
+ // below, because even if the definition is available inline, since the
+ // source specified an explicit template instantiation, we want to make
+ // the symbol available.
+ return GVA_StrongExternal;
----------------
There are a lot of commas here, making it a little hard to read the
justification.
Perhaps something along the lines of:
> This translation unit is responsible for emitting a unique instantiation of
> this function regardless of whether or not the function is marked inline.
================
Comment at: lib/CodeGen/CGVTables.cpp:744-747
@@ -743,2 +743,6 @@
case TSK_ExplicitInstantiationDefinition:
+ // If the key function has strong linkage (say due to
+ // UniqueInstantiationAttr), the VTable should too.
+ if (Context.containedInUniqueInstantiation(keyFunction))
+ return llvm::GlobalVariable::ExternalLinkage;
return !Context.getLangOpts().AppleKext ?
----------------
What if the key function is not contained within a record which is marked as
`UniqueInstantiationAttr` but the key function itself is marked
`UniqueInstantiationAttr`?
http://reviews.llvm.org/D13330
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